Pioneer work in economic entomology consisted in the determination of the insect’s life history and habits without more than casual regard to the environment in which it lived. From time to time, however, various workers have called attention to the fatal effects of the extremes of temperature and moisture, and a few persons have pursued systematic inquiry into the relations existing between temperature and insect life. Others have used various arthropods in determining the response of protoplasm to various stimuli. The last two types of investigation have proceeded far enough to show that insects in common with other organisms have minimum, optimum and maximum relations to each important stimulus to which they are subjected. More than enough work has been done to show that the life economy of the insect depends to a very large extent directly and indirectly upon the physical, chemical, and animate environment in which it lives, and that no fundamental understanding of its life economy can be reached until the effect of its environment is understood.